Superconducting accelerator cavity and method of manufacturing superconducting accelerator cavity

ABSTRACT

Provided is a superconducting accelerator cavity and a method thereof with which product reliability can be enhanced and manufacturing costs can be reduced. A method of manufacturing a superconducting accelerator cavity includes a beam-pipe forming stage of forming a beam pipe by processing a superconducting material into a tube shape; an end-plate joining stage of joining, by welding, an inner circumferential surface of an end plate formed in a shape of a ring that forms an end of a jacket, which accommodates coolant, to an outer circumferential portion of an end in the beam pipe formed in the beam-pipe forming stage; and an end-cell joining stage of joining, by welding, an iris portion of an end cell, which is formed of a superconducting material in a shape of a ring so as to form a cavity portion, to an inner circumferential portion of the end of the beam pipe.

TECHNICAL FIELD

The present invention relates to a superconducting accelerator cavityand a method of manufacturing a superconducting accelerator cavity.

BACKGROUND ART

A superconducting accelerator cavity accelerates charged particles thatpass through the interior thereof. This superconducting acceleratorcavity is formed by connecting beam pipes to ends of a cavity main body,which is a main body of the cavity, in which a plurality of cells withcircular tube shapes having swollen center portions are combined. Thecavity main body and the beam pipes are made of, for example, niobium,which is a superconducting material.

In order to maintain a superconducting state, at least the cavity mainbody needs to be kept in an extremely low-temperature state. Because ofthis, the area surrounding the cavity main body is generally surroundedby a titanium or stainless steel jacket, and the cavity main body iscooled to the extremely low-temperature state by accommodating, forexample, liquid helium inside the jacket.

At this time, it is important to maintain airtightness at joints betweenthe jacket and the superconducting accelerator cavity. Although thejoints are conventionally joined by interposing gaskets therebetween orare joined by using brazing filler metals, this has not been enough toachieve sufficient airtightness.

As disclosed in Patent Literature 1, in order to achieve sufficientairtightness, it has been proposed to provide a niobium ring withprotrusions, which has protruding portions over the entire circumferenceof an outer circumferential portion thereof, to join the titanium jacketto tips of the protruding portions by welding, followed by joining ofthe cavity main body and the beam pipes to both ends of the ring withthe protrusions by welding.

CITATION LIST Patent Literature

-   {PTL 1} Publication of Japanese Patent No. 3416249

SUMMARY OF INVENTION Technical Problem

With the disclosure of Patent Literature 1, it is necessary tomanufacture the ring with the protrusions as a member. In addition,there is a problem in that the manufacturing cost is increased becausewelding points occur at three locations when joining individual members.

Moreover, because welding at two locations, for joining the cavity mainbody and the beam pipes to both ends of the ring with protrusions, needsto be individually performed from an internal space, the weldingdirections are tilted to the joints, which makes it difficult to set thewelding positions. Because this difficult welding is required at twolocations, there is a problem in that the possibility of defectivewelding occurring due to displacement or the like is increased, and inthat the reliability of the product is decreased.

The present invention has been conceived in light of the above-describedcircumstances, and an object thereof is to provide a superconductingaccelerator cavity and a method of manufacturing a superconductingaccelerator cavity with which product reliability can be enhanced andmanufacturing cost can be reduced.

Solution to Problem

In order to solve the above-described problems, the present inventionemploys the following solutions.

Specifically, a first aspect of the present invention is asuperconducting accelerator cavity including a beam pipe that is formedof a superconducting material in a tube shape with openings at bothends; an end plate that is formed in a shape of a ring so as to form anend of a jacket, which accommodates coolant, and that is joined, at aninner circumferential surface thereof, to an outer circumferentialportion at one end of the beam pipe by welding; and an end cell that isformed of a superconducting material in a shape of a ring so as to forma superconducting accelerator cavity portion, which is a portion of thesuper conducting accelerator cavity, and that is joined, at an irisportion thereof, to an inner circumferential portion at one end of thebeam pipe by welding.

With the superconducting accelerator cavity according to the firstaspect of the present invention, the inner circumferential surface ofthe end plate that forms the end of the jacket is joined by welding tothe outer circumferential portion at the one end of the beam pipe, whichis formed in a tube shape with the openings at both ends, and the irisportion of the end cell is joined by welding to the innercircumferential portion at the one end of the beam pipe.

Because the end plate is joined with the beam pipe by welding in thisway, sufficient airtightness can be maintained under any condition.

In addition, because the end cell is directly welded to the beam pipe,welding in which the welding direction is tilted to the joint isperformed at one location. Therefore, because the probability ofdisplacement or the like occurring can be reduced, the possiblity ofdefective welding can be reduced, and the product reliability can beenhanced.

Furthermore, because rings with protrusions are not required, the numberof parts can be reduced. Accordingly, in combination with reduction inthe number of processing steps due to the fewer welding locations,manufacturing costs can be reduced.

A second aspect of the present invention is a method of manufacturing asuperconducting accelerator cavity including a beam-pipe forming stageof forming a beam pipe by processing a superconducting material into atube shape; an end-plate joining stage of joining, by welding, an innercircumferential surface of an end plate formed in a shape of a ring thatforms an end of a jacket, which accommodates coolant, to an outercircumferential portion at one end of the beam pipe formed in thebeam-pipe forming stage; and an end-cell joining stage of joining, bywelding, an iris portion of an end cell, which is formed of asuperconducting material in a shape of a ring so as to form asuperconducting accelerator cavity portion, to an inner circumferentialportion at one end of the beam pipe.

With a method of manufacturing a superconducting accelerator cavityaccording to the second aspect of the present invention, the beam pipeis formed by processing a superconducting material into the tube shapein the beam-pipe forming stage. Subsequently, in the end-plate joiningstage, the inner circumferential surface of the end plate formed in theshape of a ring so as to form the end of the jacket that accommodatescoolant is joined by welding to the outer circumferential portion at theone end of the beam pipe. Then, in the end-cell joining stage, the irisportion of the end cell formed in the shape of a ring with asuperconducting material so as to form the superconducting acceleratorcavity portion is joined by welding to the inner circumferential portionat the one end of the beam pipe.

Because the end plate is joined by welding with the beam pipe in thisway, sufficient airtightness can be maintained.

In addition, because the end cell is directly welded to the beam pipe,welding in which the welding direction is tilted to the joint isperformed at one location. Therefore, because the probability ofdisplacement or the like occurring can be reduced, the possibility ofdefective welding can be reduced and the product reliability can beenhanced.

Furthermore, because rings with protrusions are not required, the numberof parts can be reduced. Accordingly, in combination with the reductionin the number of processing steps due to the fewer welding locations,manufacturing costs can be reduced.

With the second aspect of the present invention, the beam-pipe formingstage preferably includes a deep drawing stage of processing a platematerial formed of a superconducting material into a bottom-capped tubeshape by deep drawing processing; and a first machining stage of forminga tube shape body with openings at both ends thereof by removing abottom portion of the bottom-capped tube shape, of adjusting dimensionsthereof to predetermined dimensions, and also of processing an end-platejoint to which the end plate is joined at an outer circumferentialportion at one end of the tube shape body.

With the second aspect of the present invention, a plate formed of asuperconducting material is processed into the bottom-capped tube shapeby being processed with deep drawing in the deep-drawing stage.Subsequently, in the first machining stage, the tube shape body that isopen on both ends is formed by removing the bottom portion of thebottom-capped tube shape, the dimensions thereof are also adjusted tothe predetermined dimensions, and thus, the end-plate joint to which theend plate is joined is processed at the outer circumferential portion ofthe one end of the tube shape body.

When the bottom-capped tube shape is formed by processing a platematerial by deep drawing in the deep-drawing stage, the thickness of thetube tends to become smaller toward the bottom. In other words, thethickness of the tube of the end on the open side of the bottom-cappedtube is larger than the thickness near the bottom thereof.

Because the thickness of the end plate is generally larger than thethickness of the beam pipe, when joining the inner circumferentialsurface of the end plate to the outer circumferential portion at the oneend of the beam pipe by welding in the end-plate joining stage, there isa risk of a melted portion reaching an inner circumferential side of thebeam pipe.

With the second aspect of the present invention, because the beam pipeis formed by deep drawing processing, the open side of the bottom-cappedtube shape of the tube shape body can serve as the one end, which makesit possible to suppress the risk of a melted portion reaching the innercircumferential side of the beam pipe when joining the end plate.

In the first machining stage, a flange-joint, which joins an innercircumferential portion of an attachment flange to an outercircumferential portion at the other end of the tube shape body, may beprocessed in the first machining stage.

Because a linkage or attachment flange is generally attached, bywelding, at the end (other end) of the beam pipe on the opposite sidefrom the end cell, the flange-joint for attaching this flange may beprocessed in the first machining stage.

In this case, a flange joining stage of joining the flange to theflange-joint by welding may be provided between the first machiningstage and the end-plate joining stage.

In addition, with the second aspect of the present invention, a secondmachining stage of processing a cell joint, which joins an iris portionof the end cell to an inner circumferential portion at one end of thetube shape body, may be provided before the end-cell joining stage.

By doing so, a superior cell joint, which is a joint portion of a cell,can be processed, even if, for example, deformation or the like occursat the inner circumferential surface of the beam pipe due to joining ofthe end plate.

The cell joint may be processed in the first machining stage.

Advantageous Effects of Invention

With the present invention, because the inner circumferential surface ofthe end plate that forms the end of the jacket is joined by welding tothe outer circumferential portion at the one end of the beam pipe formedin a tube shape having the openings at both ends, and because the irisportion of the end cell is joined by welding to the innercircumferential portion at one end of the beam pipe, the possibility ofdefective welding can be reduced, and the reliability of asuperconducting accelerator cavity, which is a product, can be enhanced.

In addition, because the number of parts can be reduced, in combinationwith a reduction in the number of processing steps due to the fewerwelding locations, manufacturing costs can be reduced.

BRIEF DESCRIPTION OF DRAWINGS

FIG. 1 is a front view of a superconducting accelerator cavity accordingto an embodiment of the present invention.

FIG. 2 is an explanatory diagram showing an example of a method ofmanufacturing the superconducting accelerator cavity in FIG. 1.

FIG. 3 is a cross-sectional view showing a state in which a metal plateis processed with deep drawing in a beam-pipe forming stage of themethod of manufacturing the superconducting accelerator cavity accordingto the embodiment of the present invention.

FIG. 4 is a cross-sectional view showing a state in which firstmachining has been performed in the beam-pipe forming stage of themethod of manufacturing the superconducting accelerator cavity accordingto the embodiment of the present invention.

FIG. 5 is a cross-sectional view showing flange joining in the beam-pipeforming stage of the method of manufacturing the superconductingaccelerator cavity according to the embodiment of the present invention.

FIG. 6 is a cross-sectional view showing a state of an end-plate joiningstage of the method of manufacturing the superconducting acceleratorcavity according to the embodiment of the present invention.

FIG. 7 is a cross-sectional view showing a state in which secondmachining has been performed in the method of manufacturing thesuperconducting accelerator cavity according to the embodiment of thepresent invention.

FIG. 8 is a cross-sectional view showing an end-cell joining stage ofthe method of manufacturing the superconducting accelerator cavityaccording to the embodiment of the present invention.

FIG. 9 is a cross-sectional view showing cavity-main-body joining in themethod of manufacturing the superconducting accelerator cavity accordingto the embodiment of the present invention.

DESCRIPTION OF EMBODIMENT

An embodiment of the present invention will be described below by usingFIGS. 1 to 9.

FIG. 1 is a front view of a superconducting accelerator cavity 1according to the embodiment of the present invention.

As shown in FIG. 1, the superconducting accelerator cavity 1 is providedwith a cavity portion (superconducting accelerator cavity portion) 5, inwhich, for example, nine cells 3 with circular tube shapes havingswollen center portions are combined by welding, and a pair of beampipes 7 that are attached at both ends of the cavity portion 5.

End plates 9 that form two ends of a jacket, which is a container formedso as to surround the cavity portion 5, are attached to the individualbeam pipes 7 at the cavity portion 5 sides thereof.

Although illustrations thereof are omitted, the beam pipes 7 areprovided with input ports to which input couplers are attached,higher-order-mode couplers that release higher order modes, whichinhibit acceleration of beams excited in the cavity portion 5, outsidethe cavity portion 5, and so forth.

Iris portions 11, which are the narrowest portions formed between cells3, are formed in the cavity portion 5. The cells 3 have the most-swollenportions at center portions thereof in an axial direction L. Thesemost-swollen portions will be referred to as equator portions 13.

FIG. 2 is an explanatory diagram showing an example of a method ofmanufacturing the superconducting accelerator cavity 1 in FIG. 1. Themethod of manufacturing the superconducting accelerator cavity 1 will bedescribed based on this.

First, the beam pipes 7, the end plates 9, and half cells 15 aremanufactured as individual constituent members.

The half cells 15 are the cells 3 divided into two in the axialdirection L with equator portions 13 serving as boundaries therebetween.The half cells 15 are formed by, for example, applying press molding toniobium-based material, which is a superconducting material.

A dumbbell 17 is formed by welding two half cells 15 so that thecorresponding iris portions 11 are aligned with each other. For example,eight dumbbells 17 are manufactured.

Concurrently, two end parts 19 are manufactured. The end parts 19 areformed of the beam pipes 7, the end plates 9, and half cells 15. Becausethese half cells 15 form ends of the cavity portion 5, they will behereinafter referred to as end cells 21.

The equator portion 13 at one end of a dumbbell 17 is joined with theequator portion 13 of the end cell 21 in one of the end parts 19 bywelding. The next dumbbell 17 is joined to the other end of the joineddumbbell 17 by welding. The superconducting accelerator cavity 1 isformed by repeating this and by finally joining the other end part 19.

This is merely a description of an example of the method ofmanufacturing the superconducting accelerator cavity 1, and thesuperconducting accelerator cavity 1 can be manufactured by variousmethods without limitation thereto.

A method of manufacturing the end parts 19 and structures thereof willbe specifically described below on the basis of FIGS. 3 to 8

As shown in FIG. 5, the beam pipe 7 is, for example, a hollow circularniobium tube member, and a flange 23 is provided at one end thereof.Although illustrations thereof are omitted, the beam pipe 7 is providedwith an input port, an attaching portion for a higher-order-modecoupler, and so forth.

First, a beam-pipe forming stage of manufacturing the beam pipe 7 willbe described. Raw blanks 25 shown in FIG. 3 are formed by processingniobium circular disks with a thickness of 3 to 6 mm by deep drawing(deep drawing stage). The raw blanks 25 have circular tube shapes(bottom-capped tube shapes) having bottom portions 27 and openingportions (one end) 29.

Next, a first machining stage is initiated. In the first machiningstage, the first raw blank 25 is cut at a cutting position 31 shown inFIG. 3, thus forming a tube shape body from which the bottom portion 27is removed.

Subsequently, a beam-pipe main body, which is a main body of a beampipe, 37 is formed by processing the tube shape body so that the insideand outside diameters, thicknesses, and so forth have predetermineddimensions, and by processing an end-plate joint 33 at an outercircumferential portion of an end at the opening portion 29 side and aflange joint 35 at an outer circumferential portion of an end at theopposite side from the opening portion 29.

At this time, an input port, an attaching portion for ahigher-order-mode coupler, and so forth may be processed in thebeam-pipe main body 37.

As shown in FIG. 5, for example, the niobium titanium flange 23 issubsequently joined with the flange-joint 35 of the beam-pipe main body37 by welding.

By doing so, manufacturing of the beam pipe 7 is completed.

Next, an end-plate joining stage of joining the end plates 9 with thebeam pipes 7 is initiated. The end plates 9 form both ends of a heliumjacket into which liquid helium is introduced, and the thicknesses ofinner circumferential portions of, for example, titanium end plates 19to be joined are, for example, 10 to 19 mm, which is several timesgreater than the thickness of the beam pipes 7.

As shown in FIG. 6, the end-plate joint 33 of the beam pipe 7 is alignedwith an inner circumferential surface of the end plate 9 and is heldthereat so as to form a welding groove. This welding groove isirradiated with, for example, a beam 39 to perform electron beam weldingthereat, and thus the end plate 9 is joined to the beam pipe 7. Thewelding method is not limited to electron beam welding.

In addition, although the length of the end-plate joint 33 and thethickness of the end plate 9 are made substantially equal in thisembodiment, they are not limited thereto. For example, if the length ofthe end-plate joint 33 is made longer than the thickness of the endplate 9 and, additionally, if a lower-side (opposite side with respectto the side on which the beam 39 is made incident) portion thereof isformed so as to protrude outward, because the end-plate joint 33supports the end plate 9, stable, high-quality welding can be performedmore easily.

Next, as shown in FIG. 7, a cell joint, which is a joint portion of thecell, 41 to which the iris portion 11 of the end cell 21 is joined isprocessed (second machining stage) on the inner circumferential portionof the beam-pipe main body 37 at the end thereof at the opening portion29 side.

If the cell joint 41 is processed after the end-plate joining stage inthis way, superior cell joint 41 can be processed even if, for example,deformation or the like occurs at the inner circumferential surface ofthe beam pipe 7 by being joined with the end plate 9.

The cell joint 41 may be processed in the first machining stagedescribed above.

Next, an end-cell joining stage of joining the end cell 21 to the beampipe 7 is initiated.

As shown in FIG. 8, the end cell 21 is kept so that the iris portion 11thereof fits with the cell joint 41 of the beam pipe 7. The jointbetween the end cell 21 and the beam pipe 7 is irradiated with, forexample, the beam 39 to perform electron beam welding thereat, thusjoining the end plate 9 to the beam pipe 7. The welding method is notlimited to electron beam welding.

At this time, because the beam 39 is radiated from the internal space ofthe end cell 21, the irradiation direction is tilted to the joint.

As shown in FIG. 9, the equator portion 13 of one of the half cells 15in the dumbbell 17 is joined by welding to the equator portion 13 of theend cell 21 in the end part 19 formed in this way.

The superconducting accelerator cavity 1 is manufactured by joining thedumbbells 17 in succession as described above and by finally joining theother end part 19 thereto.

Because the end plate 19 is joined by welding at the outercircumferential portion of the beam pipe 7 in this way, sufficientairtightness can be maintained.

In addition, because the end cell 21 is directly welded to the beam pipe7, welding in which the welding direction is tilted to the joint isperformed at one location. Therefore, because the probability ofdisplacement or the like occurring can be reduced as compared withmethods in which this inclined welding is performed at two locations,the possibility of defective welding can be reduced, and the reliabilityof the superconducting accelerator cavity 1 can be enhanced.

Furthermore, because rings with protrusions that are conventionallyemployed to firmly join the end plates 9 by welding are not required,the number of parts can be reduced. Accordingly, in combination withreduction in the number of processing steps due to the fewer weldinglocations, manufacturing costs can be reduced.

The present invention is not limited to the above-described embodiment,and various modifications are possible within a range that does notdepart from the spirit of the present invention.

For example, although the beam pipes 7 in this embodiment are processedinto the tube shape by employing deep drawing processing, the method isnot limited thereto. For example, the tube shape may be formed bybending rectangular plates and joining ends thereof by welding.

REFERENCE SIGNS LIST

-   1 superconducting accelerator cavity-   5 cavity portion-   7 beam pipe-   9 end plate-   11 iris portion-   21 end cell-   23 flange-   33 end-plate joint-   35 flange joint-   37 beam-pipe main body-   41 cell joint

The invention claimed is:
 1. A superconducting accelerator cavitycomprising: a beam pipe that is formed of a superconducting material ina tube shape with openings at both ends; an end plate that is formed ina shape of a ring so as to form an end of a jacket, which accommodatescoolant, and that is joined, at an inner circumferential surfacethereof, to an outer circumferential portion at one end of the beam pipeby welding; and an end cell that is formed of a superconducting materialin a shape of a ring so as to form a superconducting accelerator cavityportion and that is joined, at an iris portion thereof, to an innercircumferential portion at one end of the beam pipe by welding.
 2. Amethod of manufacturing a superconducting accelerator cavity comprising:a beam-pipe forming stage of forming a beam pipe by processing asuperconducting material into a tube shape; an end-plate joining stageof joining, by welding, an inner circumferential surface of an end plateformed in a shape of a ring that forms an end of a jacket, whichaccommodates coolant, to an outer circumferential portion at one end ofthe beam pipe formed in the beam-pipe forming stage; and an end-celljoining stage of joining, by welding, an iris portion of an end cell,which is formed of a superconducting material in the shape of a ring soas to form a superconducting accelerator cavity portion, to an innercircumferential portion at one end of the beam pipe.
 3. A method ofmanufacturing a superconducting accelerator cavity according to claim 2,wherein the beam-pipe forming stage includes a deep drawing stage ofprocessing a plate material formed of a superconducting material into abottom-capped tube shape by deep drawing processing; and a firstmachining stage of forming a tube shape body with openings at both endsthereof by removing a bottom portion of the bottom-capped tube shape, ofadjusting dimensions thereof to predetermined dimensions, and also ofprocessing an end-plate joint to which the end plate is joined at anouter circumferential portion at one end of the tube shape body.
 4. Amethod of manufacturing a superconducting accelerator cavity accordingto claim 3, wherein a flange-joint, which joins an inner circumferentialportion of an attachment flange to an outer circumferential portion atthe other end of the tube shape body, is processed in the firstmachining stage.
 5. A method of manufacturing a superconductingaccelerator cavity according to claim 4, further comprising, between thefirst machining stage and the end-plate joining stage, a flange joiningstage of joining the flange to the flange joint by welding.
 6. A methodof manufacturing a superconducting accelerator cavity according to claim3, further comprising, before the end-cell joining stage, a secondmachining stage of processing a cell joint which joins an iris portionof the end cell to an inner circumferential portion at one end of thetube shape body.
 7. A method of manufacturing a superconductingaccelerator cavity according to claim 4, further comprising, before theend-cell joining stage, a second machining stage of processing a celljoint which joins an iris portion of the end cell to an innercircumferential portion at one end of the tube shape body.
 8. A methodof manufacturing a superconducting accelerator cavity according to claim5, further comprising, before the end-cell joining stage, a secondmachining stage of processing a cell joint which joins an iris portionof the end cell to an inner circumferential portion at one end of thetube shape body.